GEOLOGY, LITHOLOGIC ASSOCIATION, AND DEPOSITIONAL ENVIRONMENT OF THE OPOSURA MASSIVE SULFIDE DEPOSIT, SONORA, MEXICO

The Oposura massive sulfide deposit is located in the Sierra La Huerta, approximately 150 km east of Hermosillo, Sonora. Stratabound and stratiform lenses of massive and thinly bedded sulfides vary in thickness from several centimeters to 3. 5 meters. Field and laboratory examinations identified four types of mineralization. The most common type consists of beds of fine-grained sphalerite and galena hosted by fine crystal tuff. It is associated with chlorite, epidote, and important amounts of manganese, either as rhodonite or rhodochrosite. The mineralization is interpreted to have formed syngenetically with deposition of crystal tuffs and limestone in a shallow subaqueous volcano-sedimentary environment.